We used to keep the boat in fresh water year round (PNW), except for a few weeks in salt water while cruising. Interlux Fiberglas Bottomkote (ablative)seemed to last at least 4-5 years. That was several years ago, not sure if they have changed the formula. Using Micron 66 now in salt water year round with good results.
SV Laurie Anne
1988 Brewer 40 Pilothouse